Having an abortion does not increase a woman's risk of suffering mental health problems, according to the world's biggest review of the issue.

It makes no difference to a woman's mental health whether she chooses to have an abortion or continue with the pregnancy, researchers found.

Women with unwanted pregnancy do have a higher incidence of mental health issues than those in the general population, but the rates of problems are the same whether a woman opts for a termination or goes on to give birth, according to the report commissioned and published by the Academy of Medical Royal Colleges.

The report, which included data on hundreds of thousands of women in 44 previous studies, was carried out by the National Collaborating Centre for Mental Health at the Royal College of Psychiatrists.

Professor Tim Kendall, director of the National Collaborating Centre for Mental Health, said 11% to 12% of the general population suffer depression and anxiety but this rises to about a third of women who have an unwanted pregnancy.

Prof Kendall said that having an unwanted pregnancy may cause mental health problems, a woman may already have problems before becoming pregnant, or it could be a combination of the two.

The experts found that women who had a history of mental health problems before having an abortion were more likely to suffer problems after the procedure.

Factors that may potentially increase the risk of mental health issues after an abortion included women being pressurised by a partner to have an abortion, stressful events, or the woman herself having a negative attitude towards abortions.

Prof Kendall said: "There is a separate debate, which is about the ethics and about legal abortion, illegal abortion, the physical consequences, which are not part of our report.

"We are simply saying that with regard to the mental health outcomes, we should now shift our attention to the problems associated with unwanted pregnancy, not abortion."